Fertility and reproductive histories of cancer patients, especially of long-term survivors of childhood and adolescent cancer, and of men and women who reproduced during cancer therapy, are studied for information on the gonadal toxicity and possible mutagenicity and teratogenicity of cancer treatment, and also to uncover hereditary patterns of cancer. Current phases include intensive analysis of data from interviews and medical records of 2498 cancer survivors and their 3604 sibling controls to learn about their subsequent health and fertility, and the health of their offspring. In 7117 offspring, 18 cancers occurred, not a significant excess over expected numbers. Survivors of childhood brain tumors were less likely to complete 8th grade, or to enter college after high school graduation. Both male and female survivors reported 30% fewer pregnancies than controls; treatment with combined radiation and alkylating agents depressed fertility in survivors to only one-third that of controls. In the subset of subjects from Kansas, survivors had more difficulty than controls getting life or health insurance. In the Connecticut subset, survivors had the same frequency of major depressive episodes as controls. A second phase is a voluntary registry of pregnancies in women with cancer. Preliminary results suggest no excess of birth defects, but some excess wastage of pregnancies conceived within 12 months of completing chemotherapy. Plans are underway for an International Conference on Reproduction and Human Cancer to be held in May 1987.